This invention relates to a filter device for use in various kinds of plants to purify a fluid by removing dust and foreign matter therefrom.
When any filter element in a filter device clogs, it has to be exchanged after stopping the flow of fluid. In order to solve this problem, a filter device was proposed which comprises a plurality of filter cases and a flow changeover device. If the filter element in one of the filter cases should clog, it can be taken out and exchanged without stopping the flow of fluid through the filter device.
This type of filter device is widely used in the industry because filter elements can be exchanged without the necessity of stopping the flow of fluid. Since it is not necessary to stop the flow of fluid, the plant does not have to be stopped and restarted each time a filter element clogs. This eliminates the related work and shortens the downtime of the plant to a minimum.
The filter devices of the type in which any clogged filter elements can be exchanged without stopping the flow of fluid can be classified into two groups according to the way in which the filter cases are cleaned and the filter elements are recycled.
(1) Only the filter elements are removed from the filter cases while leaving the filter cases coupled to the changeover device. The filter elements are recycled outside the filter device. The filter device and its peripheral parts are cleaned with a suitable solvent while the plant is kept in operation by use of another filter case. PA1 (2) The filter elements are removed from the changeover device together with the filter cases. The filter cases are disassembled and cleaned outside the filter device. PA1 1) A solvent which is classified as a dangerous substance has to be used at the site where the filter device is installed. PA1 2) Peripheral electric parts have to be made explosion-proof. This increases the installation cost. PA1 3) An inlet/outlet port for solvent has to be provided near the changeover device. This not only requires extra cost but will complicate the entire structure of the changeover device.
In the first method, since the filter cases and their peripheral parts are cleaned with a solvent, every part of the filter device can be cleaned completely and will never contaminate the fluid introduced into the device thereafter. But this method has the following problems.
The second method is safe and convenient in that the filter elements are exchanged together with their cases. This arrangement has another advantage in that the filter cases dismounted can be consigned to an outside source for cleaning. Further, the entire device is compact and inexpensive. Thus, this method is more widely employed in the art.
But the second method has a problem in that it is impossible to clean the joint portions between the changeover device and the filter cases. Heretofore, any dirt on these portions had to be wiped off with a cloth or the joint portion had to be washed by keeping a fluid running for a while after connecting the filter cases to the changeover device before starting the operation.
If the filter device is used to filter a synthetic resin that hardens while not heated, the entire device has to be heated. In such a case, heating units will be a major obstacle in cleaning the joint portions between the detachable members and the permanently fixed members. Also, it is difficult to completely wash down any dirt on such joint portions with a running fluid. This might cause frequent machine trouble after exchanging the filter element. The use of such devices cannot be adopted especially if it is necessary to remove dirt and dust of a size on the order of several microns such as in yarn reeling and film forming.